1. Field of the Invention
The present invention relates to a positioning system for locating the focus of a high-intensity focused ultrasound (HIFU) device in vivo, and more particularly to a non-invasive positioning system combining a diagnostic and a HIFU systems while being used for positioning the focus of the HIFU device in vivo.
2. The Prior Arts
Cancer has been a major threat for humans for years. Many patients are diagnosed with various tumors in their bodies every year, but frequently it's too late to resect the tumor tissues via surgical operation due to metastasis. Meanwhile, conventional chemical or radioactive therapies have limited therapeutic effects, especially for hepatoma and pancreatic cancers in the abdominal cavity. Furthermore, patients having recurrent or metastatic tumors are usually not good candidates for repeated surgical operations or chemical therapies. Patients cannot receive repeated radiotherapy due to the safety concern of radiation accumulation. Moreover, for certain benign tumors (e.g., fibroid in the uterus), space-occupying brain tumors, or metastasis, patients hope to be treated non-invasively.
Recently, the invention of high-intensity focused ultrasound for cancer therapy provides a non-invasive and effective way for tumor therapy. HIFU can induce coagulative necrosis on tumor tissues by thermal ablation, and then the necrotic tumor tissues are absorbed so as to efficiently decrease the tumor volume. For instance, the uterine fibroid, which causes over-hemorrhaging and affects the normal uterine function, can be efficiently treated by HIFU therapy without any surgical operation. Even though the uterine fibroid regenerates later, HIFU therapy can be used to treat the regenerated tissues again.
HIFU can be used to treat and remove tumor tissues in vivo in a non-invasive manner, but conventional diagnostic ultrasound provides limited images to precisely position the focus location of the HIFU device, especially when sound waves from HIFU deflect or scatter in vivo. Usually, a diagnostic ultrasound system is used to roughly position the HIFU focus on the target tumor tissues in a patient's body first. By integrating the diagnostic and HIFU transducers, the focus of HIFU is located on a pre-determined position on the obtained ultrasonic images. HIFU is then used to ablate the target region. Because the ablated regions are hyperechoic and capable of being observed by the conventional diagnostic ultrasound, it is possible to ensure if the ablated regions correspond to the locations of the tumor tissues. If the hyperechoic regions do not correspond to the locations of tumor tissues, the focus of HIFU is adjusted and the ablating procedure is repeated. However, the above method has several problems detailed in the following: (1) The ablated regions produced by HIFU generate denatured tissues which cannot be distinguished on images of the conventional diagnostic ultrasound; (2) The hyperechoes might represent an overheating situation which may damage the surrounding normal tissues; (3) Permanent damage has already been produced if observable changes, e.g., hyperechoes, on ultrasonic images were produced; (4) Since the HIFU produces interference on the diagnostic ultrasound images, HIFU cannot be used for real-time monitoring the ablation process and results. This situation is especially problematic when the tumor tissues shift during ablation (e.g., the tumor tissues adjacent to the lungs may shift due to breathing), or only a small volume is required to be precisely removed (e.g., a small volume of brain tissue); and (5) If bubbles are generated during ablations, HIFU can not penetrate the bubble cloud to treat the tumor tissue located beneath so as to reduce the actual therapeutic effect.
To ensure if the ablated regions align with the locations of the tumor tissues, magnetic resonance imaging (MRI) technology was developed to precisely position the locations of tumor tissues in a 3-dimensional manner using MRI followed by ablation using HIFU. Although the MRI technology can precisely position the locations of tumor tissues in a patient's body, the MRI scan is too expensive, occupies more operating space, and may not monitor the ablation region in real-time.
Therefore, it is important to develop a non-invasive positioning method using diagnostic ultrasound for the focus of HIFU. The non-invasive positioning system can be used to precisely position the ablated regions in real-time while efficiently preventing damage to the surrounding normal tissues.